1. Field of the Invention:
This invention relates to the bending and tempering of glass plates during their advance on a shaping bed consisting of an array of shaping rollers placed along a path to form a bed having a profile curved in the direction of advance of the glass plates.
2. Discussion of Background:
It is known from the French patent document published under No. 2 433 488 to bend and temper glass plates simultaneously by having them advance in a device consisting essentially of two layers having cylindrical rollers placed along a curved profile, blowing nozzles being inserted between the rollers. The glass plates are rolled and pressed between the rollers of the two layers and simultaneously subjected to the blowing of cold air, so that they come out bent and tempered.
This prior device possess a high production capacity, but the glass does not have the desired qualities, particularly optical quality, and exhibits certain forming defects, in particular on the front edge and the back edge of the glass plates.
Moreover, it has been proposed by the French patent document published under No. 2 549 465, to have the glass plates advance between two curved layers of rollers in a bending and tempering machine to bend said plates the first time, then to temper them the second time, blowing nozzles then being inserted between the rollers of each layer, in a downstream zone of the machine which is reserved for tempering.
In this prior device, the glass plates rest on the rollers of the lower layer and are held by the rollers of the upper layer. It no longer involves, as in the preceding case, rolling and pressing of the glass plates between lower and upper rollers, but the upper rollers nonetheless exist, and even if they are mounted flexibly with springs to avoid pressing too strongly on the glass, they touch it and so exert a certain pressure which although weak nevertheless exists and which precisely because of its desired weakness necessitates a particular mounting of said upper rollers and a fine adjustment.
A certain complexity of the machine and a necessity of performing fine positioning adjustments of the rollers of the upper layer in relation to the rollers of the lower layer result. This complexity of machine and of adjustment is further increased when the rollers used are not cylindrical but are shaping elements with variable profile in the crosswise direction of the machine, such as curved rods.
Moreover, slight support marks of the rollers or equivalent elements can be visible, mainly in the case of poor adjustments, particularly on the enamel with which the periphery or other zones of the glazings are coated, this enamel not being totally hardened at the moment of the passage into the bending machine.